Differentiate among tabs with the same name

This commit introduces a new, optional `Item::tab_description` method
that lets implementers define a description for the tab with a certain
`detail`. When two or more tabs match the same description, we will
increase the `detail` until tabs don't match anymore or increasing the
`detail` doesn't disambiguate tabs any further.

As soon as we find a valid `detail` that disambiguates tabs enough, we
will pass it to `Item::tab_content`. In `Editor`, this is implemented by
showing more and more of the path's suffix as `detail` is increased.

crates/editor/src/editor.rs

@@ -1073,7 +1073,7 @@ impl Editor {
         &self.buffer
     }
 
-    pub fn title(&self, cx: &AppContext) -> String {
+    pub fn title<'a>(&self, cx: &'a AppContext) -> Cow<'a, str> {
         self.buffer().read(cx).title(cx)
     }
 

crates/editor/src/items.rs

@@ -1,4 +1,6 @@
-use crate::{Anchor, Autoscroll, Editor, Event, ExcerptId, NavigationData, ToPoint as _};
+use crate::{
+    Anchor, Autoscroll, Editor, Event, ExcerptId, MultiBuffer, NavigationData, ToPoint as _,
+};
 use anyhow::{anyhow, Result};
 use futures::FutureExt;
 use gpui::{
@@ -10,7 +12,12 @@ use project::{File, Project, ProjectEntryId, ProjectPath};
 use rpc::proto::{self, update_view};
 use settings::Settings;
 use smallvec::SmallVec;
-use std::{fmt::Write, path::PathBuf, time::Duration};
+use std::{
+    borrow::Cow,
+    fmt::Write,
+    path::{Path, PathBuf},
+    time::Duration,
+};
 use text::{Point, Selection};
 use util::TryFutureExt;
 use workspace::{FollowableItem, Item, ItemHandle, ItemNavHistory, ProjectItem, StatusItemView};
@@ -292,9 +299,39 @@ impl Item for Editor {
         }
     }
 
-    fn tab_content(&self, style: &theme::Tab, cx: &AppContext) -> ElementBox {
-        let title = self.title(cx);
-        Label::new(title, style.label.clone()).boxed()
+    fn tab_description<'a>(&'a self, detail: usize, cx: &'a AppContext) -> Option<Cow<'a, str>> {
+        match path_for_buffer(&self.buffer, detail, true, cx)? {
+            Cow::Borrowed(path) => Some(path.to_string_lossy()),
+            Cow::Owned(path) => Some(path.to_string_lossy().to_string().into()),
+        }
+    }
+
+    fn tab_content(
+        &self,
+        detail: Option<usize>,
+        style: &theme::Tab,
+        cx: &AppContext,
+    ) -> ElementBox {
+        Flex::row()
+            .with_child(
+                Label::new(self.title(cx).into(), style.label.clone())
+                    .aligned()
+                    .boxed(),
+            )
+            .with_children(detail.and_then(|detail| {
+                let path = path_for_buffer(&self.buffer, detail, false, cx)?;
+                Some(
+                    Label::new(
+                        path.to_string_lossy().into(),
+                        style.description.text.clone(),
+                    )
+                    .contained()
+                    .with_style(style.description.container)
+                    .aligned()
+                    .boxed(),
+                )
+            }))
+            .boxed()
     }
 
     fn project_path(&self, cx: &AppContext) -> Option<ProjectPath> {
@@ -534,3 +571,38 @@ impl StatusItemView for CursorPosition {
         cx.notify();
     }
 }
+
+fn path_for_buffer<'a>(
+    buffer: &ModelHandle<MultiBuffer>,
+    mut depth: usize,
+    include_filename: bool,
+    cx: &'a AppContext,
+) -> Option<Cow<'a, Path>> {
+    let file = buffer.read(cx).as_singleton()?.read(cx).file()?;
+
+    let mut path = file.path().as_ref();
+    depth += 1;
+    while depth > 0 {
+        if let Some(parent) = path.parent() {
+            path = parent;
+            depth -= 1;
+        } else {
+            break;
+        }
+    }
+
+    if depth > 0 {
+        let full_path = file.full_path(cx);
+        if include_filename {
+            Some(full_path.into())
+        } else {
+            Some(full_path.parent().unwrap().to_path_buf().into())
+        }
+    } else {
+        let mut path = file.path().strip_prefix(path).unwrap();
+        if !include_filename {
+            path = path.parent().unwrap();
+        }
+        Some(path.into())
+    }
+}

crates/editor/src/multi_buffer.rs

@@ -14,6 +14,7 @@ use language::{
 use settings::Settings;
 use smallvec::SmallVec;
 use std::{
+    borrow::Cow,
     cell::{Ref, RefCell},
     cmp, fmt, io,
     iter::{self, FromIterator},
@@ -1194,14 +1195,14 @@ impl MultiBuffer {
             .collect()
     }
 
-    pub fn title(&self, cx: &AppContext) -> String {
-        if let Some(title) = self.title.clone() {
-            return title;
+    pub fn title<'a>(&'a self, cx: &'a AppContext) -> Cow<'a, str> {
+        if let Some(title) = self.title.as_ref() {
+            return title.into();
         }
 
         if let Some(buffer) = self.as_singleton() {
             if let Some(file) = buffer.read(cx).file() {
-                return file.file_name(cx).to_string_lossy().into();
+                return file.file_name(cx).to_string_lossy();
             }
         }